11.2.1 Preparing the Data
https://www.w3.org/community/xformsusers/wiki/XForms_2.0#Preparing_the_Data
"The binding attributes of submission are evaluated; if the result is the
empty sequence or an item other than an element or an instance document
root node, submission fails with no-data."
Presumably with serialization="none", this shouldn't fail if there's no
data. How about in the other two cases?
Steven